The present invention relates to a wire saw comprising a wire reeved about a plurality of multigrooved rollers for cutting a workpiece.
A wire saw has been known in which a wire is wound a number of turns around the outer periphery of a plurality of multigrooved rollers, and cuts a workpiece at a position between the multigrooved rollers while undergoing reciprocating motion.
The above-described wire saw is so constructed that fixed rollers and movable rollers are disposed to guide the wire between the multigrooved rollers from a wire feeding side to a wire recovery side. The wire is gradually fed to the recovery side during its reciprocation between the multigrooved rollers, which reciprocation is caused by movement of the movable rollers toward and away from the fixed rollers, thus causing the workpiece to be cut. In this cutting operation, a mixture of abrasive and lapping oil is used between the workpiece and the wire.
In order to obtain an effective cutting operation, a concentrated load must be applied to a contact area between the wire and the workpiece and the permissible tensile force on the wire must be made the most of. When using a free abrasive, a uniform permeation of a mixture of the abrasive and lapping oil is required between the wire and the workpiece. In addition, swarf must be smoothly discharged.
In the conventional wire saw, multigrooved rollers are rotatably disposed at fixed positions during the cutting of a workpiece supported on a mounting table such that the wire is held against the workpiece while moving in a straight line, thereby causing the wire B to be in linear contact with the workpiece A as shown in FIG. 10.
But this linear contact poses a problem in that a good flow of mixed fluid consisting of abrasive and lapping oil is prevented and the resistance offered against the movement of the wire is high, thus lowering the cutting effect.
In addition, other problems also occur in that, because of the linear contact, swarf cannot be discharged with ease. Thus, the cutting effect is lowered, wire tensile force is dispersed, a concentrated load cannot be exerted on the workpiece, and the permissible tension on the wire is not made the most of.
In a wire saw, it is required that the wire be wound a number of turns around outer periphery of a plurality of multigrooved rollers to form rows of wire, and that a reciprocal running motion be given to the wire being fed from the feeding side to the recovery side, resulting in wire tension and slack being alternately generated at the feeding and recovery sides with the multigrooved roller group interposed therebetween.
Thus, in a wire saw, a mechanism must be adopted to absorb the tension and slack occurring in the wire while the wire undergoes a reciprocating running motion.
A mechanism for absorbing tension and slack in the conventional wire saw is constructed in the following manner. Fixed rollers and movable rollers are disposed to guide a wire thereover, in turn, between multigrooved rollers and the wire feeding side, and between the multigrooved rollers and wire recovery side. The movable rollers are fixed to a large and heavy slide carriage which is reciprocated by a drive motor using a crank mechanism. The reciprocating motion of the slide carriage indirectly imparts to the multigrooved rollers a reversing rotary movement through an endless rope extending over the above-described fixed rollers and movable rollers. And, the wire is fed gradually toward the recovery side while it is moved back and forth at the outer periphery of the multigrooved roller group.
The following problems occur in the mechanism for absorbing tension and slack mentioned above.
(1) Because the slide carriage reciprocated by the drive motor and crank mechanism is used to absorb tension and slack resulting from the reciprocating motion of the wire, a large and heavy slide carriage must be moved, which results in a high loss of energy during the cutting operation, and imposes a limit on the speed of operation and hence the cutting accuracy.
(2) In order to drive the multigrooved rollers with a reversing rotary movement and a differential rotary motion via the movable-pulley type double-speed mechanism and crank mechanism, an endless rope is used. Since the drive system thus requires a high transmission capacity, the system must be large. This, in turn, necessitates that a long special endless rope such as a two-sided toothed belt or chain, which is expensive and not readily available, be employed for synchronizing the wire and movable-pulley type double-speed mechanism.
(3) Noise and vibration peculiar to using the above-described long, special endless rope in a high-speed operation, are generated to such a degree as to impose a limit on the speed of operation thereby diminishing cutting accuracy and the volume of work which can be carried out.
(4) Because a long special endless rope is used, the movable-pulley type double-speed mechanism must adopt specially toothed sprockets which are costly. When the number of teeth of such sprockets are few in order to make the diameter of the sprockets small for achieving a compactness of the device, fluctuations occur during the revolution of the sprockets caused by a polygonal movement peculiar thereto. Thus, such sprockets become a source of noise and vibration, cause a change in wire tension delicately driven synchronously, cause the rope to become disconnected from the drive system, and lower cutting accuracy.
(5) Due to the reciprocating motion of the wire caused by the crank mechanism, the running speed of the wire changes momentarily as a function of a sine curve, thus preventing stabilization through the uniform permeation of abrasive fluid between the workpiece and wire as well as a smooth discharge of swarf which would otherwise be usually expected by the effective utilization of the entire reciprocating portion of the wire running at a regular speed. Thus, there is a reduction in processing accuracy and a decrease in the volume of work which can be carried out.
(6) When aiming to improve cutting accuracy and increase the volume of work by increasing the speed of operation, it is desirable that the reciprocating motion of the wire preferably be carried out in a low number of cycles having long strokes to facilitate the uniform permeation of abrasive fluid, the smooth discharge of swarf, and to prevent vibrations. But, a drawback occurs in that the use of a crank mechanism in reciprocating the movable pulley unavoidably has inherent limits with respect to the radius of its revolution, and a large number of pulleys in the movable-pulley type double-speed mechanism is necessary to create a long stroke. Thus, the drive system of the device must be large and costly, and tends to give rise to vibration and maintenance problems.
(7) The drive system is so constructed that an endless rope is fed in one direction by a motor, thereby imparting differential rotary motion to the reversibly rotating multigrooved rollers through the movable-pulley type double-speed mechanism and crank mechanism in such a manner that a wire traveling synchronously with the endless rope is gradually fed from the feeding side to the recovery side of the device. Accordingly, with this mechanism, variations in the reciprocating running speed of the wire occur so that when a high-speed operation is carried out, variations in the reciprocating running speed of the wire become all the more remarkable, whereby stabilization due to uniform permeation of abrasive fluid between the workpiece and wire, which is enhanced by a constant running speed of the wire, is nonetheless prevented, whereby swarf cannot be smoothly discharged. Thus, the cutting accuracy is lowered and the volume of work to be carried out is decreased.